In the past decade, the back-to-nature movement has taken a called third strike in the major leagues, where nine of 26 parks have gone "artificial." The list includes those stadiums in Philadelphia and Kansas Series, the first ever played entirely on artificial "turf."

The new fields have practically revolutionized the game, turning what might be routine grounders on grass into base hits. And what may appear to be relatively harmless line drives wind up reaching the farthest outfield walls while whippet runners circle the bases.

In the current series, Kansas City is considered the prototype artificial turf team -- one with the all-around speed to cut off the opposition's bullet-like grounders or squeeze extra bases out of their own.

Philadelphia's Del Unser, a veteran of five major league clubs, says playing on synthetic fields is "quite an adjustment. Your reflexes have to be sharp. Kansas City's at a distinct advantage playing on their artificial turf. Their outfielders get to the ball quickly and the shortstop [U. L. Washington] and second baseman [Frank White] are very fast.

"Another club that's done a beautiful job of fitting its personnel to the [ home] park is Houston, which has three deer in the outfield."

Houston, which lost to the Phillies in the National League playoffs, is quartered in the Astrodome, where artificial turf first sprang into existence.

Originally the Astrodome was to have grass, but it didn't get enough sunlight to grow, and what light did filter in often reflected off the glass panes into the filders' eyes. The panes were sealed over and Monsanto of St. Louis contracted to develop a synthetic turf. The success of Astro turf and similar surfaces prompted many stadium authorities to pave over their cross-mowed emerald lawns and lay durable, low-maintenance surrogates.

Some facilities have had second thoughts, however. In San Frlancisco's Candlestick Park the artificial turf was ripped up and replaced with grass, a scene repeated in Chicago's Comiskey Park and Miami's football Orange Bowl.

There are various reasons for either sticking with natural turf or converting back to it. Aesthetically, nothing beats the lush beautyl of the real McCoy. In addition, grass is softer and cooler than the clinical-looking synthetic surfaces, which sit on beds of cushioned asphalt.

The artificial fields can be unpopular with football players, who find them inhospitable crash pads. Even running on them can be uncomfortable if one isn't wearing the right kind of shoes. During the baseball playoffs, for example, Houston's Joe Morgan wore cleats while batting, but slipped into nub-bottomed shoes on the basepaths.

The infield has been covered over on most artificially surfaced baseball diamonds, with dirt "sliding pits" and batter's boxes practically the only cutouts in the carpet.

The uniformity that results, some feel, is a plus for baseball. With so few bad hops, Kansas City's White says, "the fans get to see a better-played game." Others, however, would argue there are just as many bad hops on artificial turf as on grass.

The high bounces, or "Baltimore chops,c can probably be beaten out mor easily than a bunt, which now skids along the synthetic field instead of dying onthe grass.

Because grounders lose so little speed, says Philadelphia shortstop Larry Bowa, "you tend to get a little lzy on this stuff [artificial turf].IT's so quick, you lay back and wait for teh ball to come to you."

Both infielders and outfielders must position themselves intelligently and play deeper to allow extra time to get in front of these speeding bullets. Consequently, many more hits drop in front of the outfielders. Where these players may now have an offsetting advantage is on their throws to the plate, which bounce fast and true.

Outfielders aren't the only ones to capitalize on this feature. Cincinnati shortstop Dave Concepcion has mastered a one-hop throw to first for those occasions when he's too far away to execute a conventional one.

Concepcion, by the way, appeared in several World Series played partially onthe artificial turf of Cincinnati's Riverfront Stadium in the 1970. And last year, Pittsburgh's world champion Pirates hosted three games on their carpet in Three Rivers Stadium.